05 March, 2021
Plant cognition
- Do plants sense their environment?
- changes in essential resources
- herbivory/disturbance
- external stimulus
- If so, what do they do about it?
- do plants process information?

Sensory cell systems


- Cell to cell signal networks
- Ca2+ based signals are common
Wounding triggers transmission of Ca2+ to start defense

Plants grow towards light: Phototropism via Auxin


Plants competing for light can grow really tall

- Primary and secondary growth allow trees to be giants
- Are their limitations to plant height?
- What resource most limits growth?
Plant Water Transport: Soil - Root - Stem - Leaf - Air


Are there limits to moving water?

- Large trees move hundreds of gallons of water a day
- only small amounts needed for growth/photosynthesis
- Gravity
- harder and harder to move water
- xylem less efficient @ top
- theoretically, limits growth to 122-130 m
- Drying soil adds opposite tension
How long a straw could Superman use?


How can redwood trees grow so tall?
- Cohesion tension theory
- plants use water properties to cheat gravity
- Cohesion: H20 stick to other H20 molecules
- Adhesion: water sticks to non water molecules
- stick to sides of xylem tissues
- H20 not pulled straight up!
- Transpiration pulls water under tension

How can redwood trees grow so tall?
- H2O also pulled in zig zag motion
- pits and perforations
- tracheids are twisted
- Vascular tissue is tough
- high resistance of lignified walls
- built not to collapse
- Redwoods near theoretical limit!

Cavitation: When water breaks




How plants avoid water problems: Close stomata

Risky stomatal behavior

How plants avoid water problems: Refill Soil


How plants avoid water problems: Alter xylem cells

